Piston design for flow re-direction

ABSTRACT

An internal combustion engine includes an engine block having a cylinder bore and a cylinder head having a flame deck surface disposed at one end of the cylinder bore. A piston connected to a rotatable crankshaft and configured to reciprocate within the cylinder bore has a piston crown portion facing the flame deck surface such that a combustion chamber is defined within the cylinder bore and between the piston crown and the flame deck surface. A fuel injector having a nozzle tip disposed in fluid communication with the combustion chamber has at least one nozzle opening configured to inject a fuel jet into the combustion chamber along a fuel jet centerline. At least one arcuate indent is formed in the top surface in aligned fashion with the fuel jet and including an entry surface, a recirculation surface and a wall.

TECHNICAL FIELD

This patent disclosure relates generally to internal combustion enginesand, more particularly, to combustion chamber features for directinjection engines.

BACKGROUND

Most modern engines are direct injection engines, which means that eachcombustion cylinder of the engine includes a dedicated fuel injectorconfigured to inject fuel directly into a combustion chamber. Whiledirect injection engines represent an improvement in engine technologyover past designs, in the form of increased engine efficiency andreduced emissions, the improvement of the design of any particularengine is always desirable, especially in light of increasing fuel costsand ever more strict regulations on engine emissions.

In a traditional direct injection engine, one or more fuel jets that areinjected into a combustion chamber interact with various combustionchamber structures, which cause the fuel to disperse into the combustionchamber. More specifically, the fuel jet(s) entering the combustionchamber impact various surfaces of the combustion chamber such as apiston bowl, the flame deck surface of the cylinder head, the cylinderliner or bore, and other surfaces before spreading in all directions.The impingement of the fuel jets with these structures may have avariety of effects including increased emissions because localized areashaving higher fuel concentrations may burn rich while other areas on thecylinder may burn lean. This can further result in higher temperatures,decreased fuel efficiency, increased heat rejection and componenttemperatures, and the like.

Various solutions have been proposed in the past for improving anengine's efficiency and reducing its emissions. One example of apreviously proposed solution can be seen in U.S. Pat. No. 9,091,199(“Straub”), which was granted on Jul. 28, 2015. Straub describes acombustion chamber that includes a piston forming deflection foils. Thedeflection foils, according to Straub, operate to distribute a fuelspray into portions directed toward one of the deflection foils, whichredirect their respective portion of the fuel spray into a combinedradial path that swirls about a center of the combustion. In thedescribed embodiment, Straub explains that the fuel spray is thusdirected substantially tangential relative to the combined radial pathof the redirected portions of the fuel spray. While the flow redirectionof Straub may be partially effective in improving mixing of air withincoming fuel in the combustion chamber, the momentum of the redirectedfuel spray is maintained generally parallel to a top piston surface suchthat the induced swirling may cause fuel to migrate towards a cylinderwall. Maintaining the fuel close to the piston may also increase heatrejection while the fuel is burning.

SUMMARY

The disclosure describes, in one aspect, an internal combustion engine.The internal combustion engine includes an engine block having at leastone cylinder bore, a cylinder head having a flame deck surface disposedat one end of the cylinder bore, a piston connected to a rotatablecrankshaft and configured to reciprocate within the cylinder bore, thepiston having a piston crown portion facing the flame deck surface suchthat a combustion chamber is defined within the cylinder bore andbetween a top surface of the piston crown and the flame deck surface,and a fuel injector having a nozzle tip disposed in fluid communicationwith the combustion chamber, the nozzle tip having at least one nozzleopening configured to inject a fuel jet into the combustion chamber andalong a fuel jet centerline. At least one arcuate indent is formed inthe top surface. The at least one arcuate indent is aligned with thefuel jet centerline and includes an entry surface extending from acentral portion of the piston, a recirculation surface having a concaveshape and extending along a spiral direction adjacent the entry surface,and a wall extending generally in an axial direction and disposedradially along the recirculation surface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross section of an engine combustion chamber in accordancewith the disclosure.

FIG. 2 is a top view of an engine piston in accordance with thedisclosure.

FIG. 3 is a perspective view of a top surface of a piston in accordancewith an alternative embodiment.

FIG. 4 is a schematic view of a top surface of a piston during varioustimes in operation.

DETAILED DESCRIPTION

This disclosure relates to internal combustion engines and, moreparticularly, to features incorporated within at least one combustionchamber of the engine to contain and redirect fuel jets provided byseparate fuel injector nozzle openings. The fuel jets are redirected andalso segregated during a majority of the injection time to promotebetter fuel/air mixing and a more uniform fuel/air mixture within thecombustion chamber as compared to previously proposed or knowncombustion systems. The various exemplary embodiments described hereininclude structures and features that operate or result in redirectingfuel jets circumferentially with respect to the cylinder bore of anengine, to thus avoid, minimize or, at least, delay interaction betweenadjacent fuel jets entering the combustion chamber. The type of fuelbeing provided to the cylinder may be a spray of liquid fuel such asdiesel or gasoline, or a jet of gaseous fuel such as natural orpetroleum gas. The design features redirect each fuel jet separately tocreate a spiral motion within the combustion chamber independently fromany swirl generated from the use of valve inserts or port designchanges. In the described embodiments, this is accomplished, at least inpart, by directing an impact or impingement of one or more jets ofcombusting fuel towards an interior of the combustion chamber and awayfrom the cylinder head, the valves, and the cylinder liner. Thecombustion and heat release are, in this fashion, kept away fromsurfaces and insulated within the combustion chamber by the surroundingfluids within the combustion chamber, which in turn leads to lowercomponent temperatures, increased fuel efficiency, and a more uniformfuel/air mixture, which also leads to lower engine emissions.

A cross section of a combustion chamber 100 of an engine 101 inaccordance with the disclosure is shown in FIG. 1. The combustionchamber 100 has a generally cylindrical shape that is defined within acylinder bore 102 formed within a crankcase or engine block 104 of theengine. The combustion chamber 100 is further defined at one end by aflame deck surface 106 of a cylinder head 108, and at another end by apiston crown 110 of a piston 112 that is reciprocally disposed withinthe bore 102. A fuel injector 114 is mounted in the cylinder head 108.The injector 114 has a tip 116 that protrudes within the combustionchamber 100 through the flame deck surface 106 such that it can directlyinject fuel into the combustion chamber 100.

During operation of the engine 101, air is admitted into the combustionchamber 100 via an air inlet passage 115 when one or more intake valves117 (one shown) are open during an intake stroke. In a knownconfiguration, high pressure fuel is permitted to flow through nozzleopenings in the tip 116. Each nozzle opening creates a fuel jet 118 thatgenerally disperses to create a predetermined fuel/air mixture, which ina compression ignition engine auto-ignites and combusts. The fuel jets118 may be provided from the injector at an included angle, β, ofbetween 110 and 150 degrees, but other angles may also be used.Following combustion, exhaust gas is expelled from the combustionchamber through an exhaust conduit 120 when one or more exhaust valves122 (one shown) is/are open during an exhaust stroke.

The uniformity and extent of fuel/air mixing in the combustion cylinderis relevant to the combustion efficiency as well as to the amount andtype of combustion byproducts that are formed. For example, fuel-richmixtures, which may be locally present within the combustion chamber 100during a combustion event due to insufficient mixing, may lead to highersoot emissions and lower combustion efficiency. In the illustratedembodiments, more-uniform fuel/air mixing is managed for each fuel jetby forming a plurality of arcuate indents symmetrically around and intothe crown surface of the piston. Each arcuate indent serves to accept,contain, redirect and segregate therein one of a plurality of fuelstreams originating from one of a plurality of nozzle openings in thefuel injector from mixing with other fuel streams from the remainingnozzle openings, at least for a period, during an injection and/or fuelburning event in the combustion chamber during operation. Each arcuateindent presents a cambered, pitched face on the top surface of thepiston, which leads into a concave feature formed or otherwiseconstructed into the top piston face.

An exemplary embodiment of the piston 112 is shown in FIG. 2. In theillustration of FIG. 2, only a top surface 200 of the piston crown 110of the piston 112 is shown for simplicity. The top surface 200 has agenerally circular shape that encloses a crown surface 202. The topsurface 200 is defined within a circular periphery 204 and has agenerally flat shape that extends along a single plane 206 that isnominally disposed in perpendicular relation to a centerline axis of thebore 102 (FIG. 1). Included within the top surface 200 is a plurality ofarcuate indents 208, which have a concave shape extending away from theplane 206 in a direction into the body of the piston 112 (i.e., in adownward direction in the orientation shown in FIG. 1). In theillustrated embodiment, five arcuate indents 208 are shown, but fewer ormore arcuate indents can be used on any one particular piston. In use,it is contemplated that there will be as many arcuate indents as nozzleopenings in the injector tip such that each fuel jet provided by theinjector will correspond to one arcuate indent of the piston. It shouldalso be appreciated that not all arcuate indents might have the sameshape. In this embodiment, the fuel injector 114 (FIG. 1) includes fivenozzle openings formed in the tip 116 such that five fuel jets 118 areproduced during engine operation. As shown, all five arcuate indents 208have the same shape to redirect the five fuel jets 118 provided by theinjector in the same of a similar, symmetrical fashion. When the piston112 is reciprocally mounted in the bore 102 of the engine 101, the topsurface 200 is oriented such that each of the fuel jets 118 is injectedin a direction such that the fuel jet 118 enters into a respectivearcuate indent 208 to be redirected thereby during engine operation.

Each arcuate indent 208 presents various flat, concave or convexsurfaces, which directly or indirectly redirect the respective fuel jetprovided into the arcuate indent 208 during operation. In theillustrated embodiment, each arcuate indent 208 includes a flat, entrysurface 210. For each particular arcuate indent 208, the entry surface210 lies along a plane that is disposed at an acute angle relative tothe plane 206 of the piston crown. The entry surface 210 has a generallytriangular shape with curved edges that includes a central point 212disposed adjacent a piston surface center 214. The entry surface 210extends away from the piston surface center 214 in a radial directionalong the angled plane to provide a cambered or pitched surface that,during operation, engages and contacts the respective fuel jet to directit along the plane and into the arcuate indent 208.

Opposite the central point 212, the entry surface 210 has a generallycurved edge 216 that is sickle-shaped and may include a break orinflection, which forms a transition between the entry surface 210 and arecirculation surface 218. The recirculation surface 218, which forms abottom-most portion of the arcuate indent 208, has a concave shape thatsweeps in a spiral direction radially outwardly from the piston centerportion along the curved edge 216. A cross section available for fueljet redirection of the recirculation surface 218 is maximum along amiddle portion thereof, adjacent a second point 220 of the entry surface210, and decreases in both radial directions inwardly and outwardly withrespect to the piston center portion such that it becomes minimumadjacent each of a third point 222 and the central point 212 of thegenerally triangular entry surface 210.

Each arcuate indent 208 further includes a wall 224 extending generallyparallel or at a slight angle relative to a piston crown centerline orsymmetry axis. The wall 224 has a variable width or height that isminimum along the wall's radially inward and outward ends, and maximumalong a middle portion thereof. The wall 224 presents a top edge 226having a generally curved shape and a bottom edge 228 that follows anexternal edge of the recirculation surface 218. At an interface or rimof each arcuate indent 208 with respect to the flat crown surface 202 isdisposed a convex transition 230. A plurality of depressed surfaces 232that bow away from the plane 206 of the crown surface 202 may also beformed around the piston such that the piston surface center 214protrudes as a peak relative to the surrounding arcuate indents 208.When the top surface 200 of the piston is viewed from an overallperspective, the arrangement of the arcuate indents 208 resembles aflower or, when viewed differently, one side of a negative mold for awater propeller.

An alternative embodiment for a top surface 300 of a piston inaccordance with the disclosure is shown in FIG. 3. In this embodiment,the same or similar features and structures as the top surface 200 (FIG.2) are denoted by the same reference numerals previously used forsimplicity. The top surface 300, similar to the top surface 200,includes an arrangement of five arcuate indents 208, but in thisembodiment, a transition between indents in a radially outward region302 is truncated to create a segmented circular periphery 310 thatsurrounds the central depression around the piston surface center 214.For comparison, in the top surface 200, there is no pronounced peripherysuch that the flat crown surface 202 extends between the indents formingsharp angles 234.

The top surface 300 further includes a frusto-conical outer surface 304,which creates an empty space around a top, outer periphery of thepiston. The outer surface 304 opens up the squish-region of the piston,that is, the region along the outer peripheral cylindrical surface ofthe piston that is disposed above the upper seal ring of the piston andoccupies the cylindrical space between the piston and the inner surfaceof the piston bore. In the illustrated embodiment, the outer surface 304extends at an acute angle, a, between a top edge 306 of the outercylindrical portion of the piston crown and an outer periphery 308 ofthe flat crown surface 202, and occupies a height, H, in an axialdirection along the centerline of the piston crown. It is contemplatedthat the angle, α, can be between 0 and 60 degrees, but other angles mayalso be used.

INDUSTRIAL APPLICABILITY

The present disclosure is not only applicable to internal combustionengines having reciprocating pistons, as described relative to theembodiments illustrated herein, but also to other types of applications,such as gas turbines, industrial burners and the like. In general thevarious arcuate indents can be formed in a structure that the fuel willimpinge upon when injected by an injector into a combustion chamber. Thearcuate indents and the redirection and segregation of fuel jets andplumes they provide are effective in promoting faster and more uniformpremixing of fuel and air in the combustion chambers of engines, andinhibit the entrainment of recirculated combustion products fromdownstream regions into upstream regions of a fuel jet injected into thecombustion chamber.

A time-lapse representation of the engagement and redirection of a fueljet 118 in an arcuate indent 208 is shown for five time instances, allof which are represented together for illustration, in FIG. 4. Thepiston shown in FIG. 4 is segmented into five areas, a first area,denoted by “(1),” a second area, denoted by “(2),” a third area, denotedby “(3),” a fourth area, denoted by “(4)” and a fifth area, denoted by“(5).” While shown on a single piston, it should be appreciated thateach of the first through fifth areas represents a snapshot of theposition and distribution of a fuel jet in different instances of time,and also represent a different position of the piston in the bore,beginning at about −5 degrees after top dead center (dATDC), which canalso be expressed as 5 degrees before top dead center (dBTDC), to about30 dATDC. Of course, it should be appreciated that the distribution ofthe fuel jet and it interaction with the arcuate indent may changedepending on the fuel injection timing of a particular engineapplication and combustion system.

Table 1 below illustrates the particular timing shown in theillustration of FIG. 4.

TABLE 1 Position No. Timing (dATDC) (1) −5 (2) −2 (3)  4 (4) 14 (5) 28

In reference now to FIG. 4, it can be seen that at the initiation of afuel injection at the first position, a fuel jet 118 is provided at theentrance of an arcuate indent 208 at an entrance of floor angle 402,which can be between about 15 and 30 degrees with respect to the plane206 of the top surface or crown surface 202. The entrance or floor angle402 depends on the inclination of the entry portion of the arcuateindent and/or the inclination of the nozzle openings in the particularfuel injector providing the fuel jet and the axial position of thepiston within the bore. As will be described below, the fuel will exitthe arcuate indent at an exit angle 404, which depends on the shape ofthe radially outward portion of the indent and defines an interaction ofthe fuel jet with the cylinder head and the adjoining jets. The exitangle 404 in the illustrated embodiment can be between 10 and 60degrees.

At the second position, which occurs moments after the first position,the fuel jet has contacted the recirculation surface and begins tospread into a wider region of contact 406 as fuel from the jet isredirected by contacting the recirculation surface. As the redirectedfuel follows the recirculation surface, it will reach a depth 418 thatis between 5 and 20 percent of the bore diameter, and turn around a bendradius 410 that is about 5 and 30 percent of the bore diameter. At thesame time, the fuel will be redirected upwards and away from the pistonface, in a re-entrant direction 422, which will create an inward motionof the fuel plume created from the jet that overhangs the trailingportion of the jet by between 0 and 12 percent of the radial lengthoccupied by the jet and resulting plume. Because the radial location atwhich the fuel jet enters and exits the arcuate indent will changedepending on the axial distance of the piston from the fuel injectornozzle openings, a radial entrance position 414 may be between 0 and 31percent of the bore diameter, while a radial exit position 416 may bebetween 5 and 50 percent of the bore diameter.

Accordingly, at the third position, the fuel jet has continued and theregion of the jet that has been redirected 408 has extended to occupy alarger portion of the recirculation surface. It is noted that a radialcomponent of the velocity or momentum of the fuel jet causes the fuel tofollow the recirculation surface as a redirected jet 408, which nowforms a stream, moves in a radially outward and spiral path.

At the fourth position, the redirected jet 408 reaches an end of thearcuate indent and its momentum carries away from the piston to form aplume 424 that is directed in an upward direction away from the piston.Because of the shape of the redirected jet feeding the plume creation,the plume tends to concentrate in one direction that does notimmediately infringe or stray in a direction of a neighboring plumecreated by an adjacent arcuate indent. In this way, the various plumesare segregated as the fuel jets are redirected to permit better fuel/airmixing in the combustion chamber, as previously described.

At the fifth position, a majority of the fuel provided from the injectoris now present in a plume 412 that has mostly exited the arcuate indentin an “upward” direction or, stated differently, in a direction awayfrom the piston face and towards the interior portion of the combustionchamber while the jet is already burning or is about to begin burning.As can be seen from the illustration of FIG. 4, some of the radialcomponent of the momentum of the fuel may cause the plume 412 to driftin a radially outward direction. In addition to some radial outwardmotion, the plum has left the piston with some upward trajectory awayfrom the piston such that the plume is still segregated or mostly orgenerally separated from mixing with plumes of adjacent arcuate indents.

It will be appreciated that the foregoing description provides examplesof the disclosed system and technique. However, it is contemplated thatother implementations of the disclosure may differ in detail from theforegoing examples. All references to the disclosure or examples thereofare intended to reference the particular example being discussed at thatpoint and are not intended to imply any limitation as to the scope ofthe disclosure more generally. All language of distinction anddisparagement with respect to certain features is intended to indicate alack of preference for those features, but not to exclude such from thescope of the disclosure entirely unless otherwise indicated.

Recitation of ranges of values herein are merely intended to serve as ashorthand method of referring individually to each separate valuefalling within the range, unless otherwise indicated herein, and eachseparate value is incorporated into the specification as if it wereindividually recited herein. All methods described herein can beperformed in any suitable order unless otherwise indicated herein orotherwise clearly contradicted by context.

We claim:
 1. An internal combustion engine, comprising: an engine blockhaving at least one cylinder bore; a cylinder head having a flame decksurface disposed at one end of the cylinder bore; a piston connected toa rotatable crankshaft and configured to reciprocate within the cylinderbore, the piston having a crown portion facing the flame deck surfacesuch that a combustion chamber is defined within the cylinder bore andbetween a top surface of the crown portion and the flame deck surface; afuel injector having a nozzle tip disposed in fluid communication withthe combustion chamber, the nozzle tip having at least one nozzleopening configured to inject a fuel jet into the combustion chamber andalong a fuel jet centerline; at least one arcuate indent formed in thetop surface, the at least one arcuate indent being aligned with the fueljet centerline and including an entry surface extending from a centralportion of the piston, a recirculation surface having a concave shapeand extending along a spiral direction adjacent the entry surface, and awall extending generally in an axial direction and disposed radiallyalong the recirculation surface.
 2. The internal combustion engine ofclaim 1, wherein the top surface has a generally circular shape that isdefined within a circular periphery and has a generally flat shape thatextends along a single plane that is nominally disposed in perpendicularrelation to a centerline axis of the cylinder bore.
 3. The internalcombustion engine of claim 2, wherein the piston forms a plurality ofarcuate indents arranged to cover the crown portion in aligned relationwith a plurality of nozzle openings formed in the nozzle tip of the fuelinjector.
 4. The internal combustion engine of claim 2, wherein the atleast one arcuate indent has a concave shape extending away from theplane in a direction into a body of the piston, and wherein the at leastone arcuate indent presents flat, concave or convex surfaces, whichdirectly or indirectly redirect the fuel jet provided into the arcuateindent during operation of the internal combustion engine.
 5. Theinternal combustion engine of claim 2, wherein the at least one arcuateindent includes a flat, entry surface.
 6. The internal combustion engineof claim 5, wherein the entry surface lies along an angled plane that isdisposed at an acute angle relative to the plane of the top surface. 7.The internal combustion engine of claim 6, wherein the entry surface hasa generally triangular shape with curved edges that includes a centralpoint disposed adjacent a piston surface center, and wherein the entrysurface extends away from the piston surface center in a radialdirection along the angled plane to provide a cambered or pitchedsurface that, during operation, engages and contacts a respective fueljet to direct it along the plane and into the arcuate indent.
 8. Theinternal combustion engine of claim 6, wherein, opposite a central pointof the top surface, the entry surface has a generally curved edge thatis sickle-shaped, which forms a transition between the entry surface andthe recirculation surface.
 9. The internal combustion engine of claim 1,wherein recirculation surface forms a bottom-most portion of the arcuateindent.
 10. The internal combustion engine of claim 9, wherein therecirculation surface has a concave shape that sweeps in the spiraldirection radially outwardly from a center portion of the piston along acurved edge of the entry surface.
 11. The internal combustion engine ofclaim 10, wherein a cross section available for fuel jet redirection ofthe recirculation surface is maximum along a middle portion thereof anddecreases in both radial directions inwardly and outwardly with respectto the piston.
 12. The internal combustion engine of claim 1, whereinthe wall has a variable height that is minimum along radially inward andoutward ends of the wall, and is maximum along a middle portion thereof.13. The internal combustion engine of claim 12, wherein the wallpresents a top edge having a generally curved shape and a bottom edgethat follows an external edge of the recirculation surface.
 14. Theinternal combustion engine of claim 1, wherein at an interface or rim ofthe at least one arcuate indent with respect to the top surface isdisposed a convex transition.
 15. The internal combustion engine ofclaim 1, further comprising a depressed surface that bows away from aplane of the crown portion.
 16. The internal combustion engine of claim1, further comprising a plurality of arcuate indents arrangedsymmetrically around the piston, wherein a transition between adjacentarcuate indents in a radially outward region is truncated to create asegmented circular periphery that surrounds a central depression definedaround a piston surface center.
 17. The internal combustion engine ofclaim 1, further comprising a plurality of arcuate indents arrangedsymmetrically around the piston, wherein a transition between adjacentarcuate indents in a radially outward region forms sharp angles.
 18. Theinternal combustion engine of claim 1, further comprising a recessedupper edge that creates an empty space around a top, outer periphery ofthe piston, which opens up space above a region along an outerperipheral cylindrical surface of the piston that is disposed above anupper seal ring of the piston and occupies a cylindrical space betweenthe piston and an inner surface of the cylinder bore.
 19. The internalcombustion engine of claim 18, further comprising a frusto-conicalsurface extending at an acute angle between a top edge of the outerperipheral cylindrical surface of the crown portion and an outerperiphery of the top surface.
 20. The internal combustion engine ofclaim 19, wherein the frusto-conical surface occupies a height in anaxial direction along a centerline of the crown portion.